Problem 95 - Objective Biology for NEET

Question

Which of the following events do not occur during joint diastole? A. All four chambers of heart are in relaxed state. B. Tricuspid and bicuspid valves open. C. Action potential is conducted from SAN to AVN. D. Blood from the pulmonary veins and vena cava flows into the left and right ventricles respectively through the left and right atria. \(\mathrm{E}\). The semilunar valves are closed. (a) Only E (b) Only \(\mathrm{C}\) (c) Only D (d) Only \(\mathrm{A}\) and \(\mathrm{B}\)

Step-by-Step Solution

Answer

Option (b) Only C does not occur during joint diastole.

Step 1: Understanding Joint Diastole

Joint diastole is the period during the cardiac cycle when the atria and ventricles are both relaxed and filling with blood. During this time, the semilunar valves are closed to prevent backflow of blood into the heart, thus option E is a correct event during this phase.

Step 2: Identify Incidents During Joint Diastole

Option A indicates that all four chambers are in a relaxed state, this is true, because that is what a joint diastole means, so A does occur. Option B, the tricuspid and bicuspid valves open, is also true, because these valves must be open for blood flow into the ventricles for filling. Option D, blood from the pulmonary veins and vena cava flows into left and right ventricles respectively is also true as blood flows passively from these vessels into the ventricles.

Step 3: Identifying the Non-occuring Event

This leaves option C, which states action potential is conducted from the Sinoatrial Node to the Atrioventricular Node, as the only event that does not occur during joint diastole. During this time the heart is resting and no action potential is being conducted.

Key Concepts

Joint Diastole

In the cardiac cycle, joint diastole is a unique phase when both the atria and ventricles of the heart are in a relaxed state. This is crucial as it allows the heart chambers to fill with blood adequately, preparing it for the next phase of contraction, or systole. During this stage, the heart is effectively in a quiescent period, and it is essential for maintaining the heart's efficiency and functionality.

Key events during joint diastole include:

• All four chambers, both atria and ventricles, are completely relaxed, allowing for the influx of blood.
• Blood flows from the major veins – the pulmonary veins and the vena cavae – into the atria, and subsequently into the ventricles.
• There is no conduction of action potential; the heart's electrical activity is at rest.
• The semilunar valves remain closed, while the atrioventricular valves (tricuspid and bicuspid) are open, promoting the passive flow of blood into the ventricles.

This period is vital because it ensures that the heart chambers refill with blood in preparation for the next heartbeat.

Heart Chambers

The heart consists of four chambers, each playing a crucial role in maintaining efficient blood circulation throughout the body. These chambers function as a cohesive unit during each cardiac cycle.

The four chambers include:

• The Right Atrium: Receives deoxygenated blood from the body through the superior and inferior vena cavae.
• The Right Ventricle: Pumps this deoxygenated blood to the lungs via the pulmonary artery for oxygenation.
• The Left Atrium: Receives oxygen-rich blood from the lungs through the pulmonary veins.
• The Left Ventricle: The powerhouse chamber that pumps oxygenated blood to the entire body through the aorta.

Each chamber operates in a coordinated manner, where the atria and ventricles contract and relax in continuous cycles, ensuring the efficient flow of blood.

Valves of the Heart

The valves of the heart are essential components that ensure unidirectional blood flow and prevent any backflow. There are four primary valves in the heart, each designed to open and close efficiently during different phases of the cardiac cycle.

The four main heart valves include:

• Tricuspid Valve: Located between the right atrium and right ventricle, it prevents backflow into the atrium when the ventricle contracts.
• Bicuspid (Mitral) Valve: Situated between the left atrium and left ventricle, it ensures one-way blood flow during the contraction of the ventricle.
• Pulmonary Valve: Controls blood flow from the right ventricle into the pulmonary artery, leading to the lungs.
• Aortic Valve: Positioned between the left ventricle and aorta, it regulates blood flow into the aorta and onward to the body.

These valves open and close in response to pressure differences in the heart chambers, coordinating perfectly to facilitate effective circulation.

Action Potential in Heart

The action potential in the heart is the electrical impulse that initiates the contraction of the heart muscle. This electrical activity is vital for the heart's rhythmic and synchronized contraction, ensuring efficient pumping of blood.

Key points about action potential include:

• The process begins at the Sinoatrial Node (SAN), known as the heart's natural pacemaker, located in the right atrium.
• This impulse travels to the Atrioventricular Node (AVN), then down the Bundle of His and through the Purkinje fibers to stimulate the ventricles.
• During joint diastole, the heart experiences no action potential as the chambers are resting.
• Proper initiation and conduction of action potentials are crucial to avoid arrhythmias or irregular heartbeats.

The coordinated spread of action potential ensures that the heart contractions occur in a precise and timely manner, which is essential for maintaining consistent circulation and blood supply throughout the body.